This invention relates to a control system for a motor vehicle non-stage transmission, and more particularly to an electronic control system for controlling the operation of a V-belt type non-stage transmission.
A non-stage transmission control system of this type has been disclosed by Unexamined Japanese Patent Application (Kokai) Sho-62-31533/(1987). The conventional non-stage transmission control system is as shown in FIG. 4. In FIG. 4, reference numeral 1 designates a transmission hydraulic pressure controlling solenoid valve; and 2, a main hydraulic pressure controlling solenoid valve. Each of those solenoid valves is of output hydraulic pressure feed-back type; that is, its output hydraulic pressure is controlled on the balance between itself and the electromagnetic suction force thereof.
Further in FIG. 4, reference numeral 11 designates output hydraulic pressure feedback paths; 12, electromagnetic coils; 13, casings; and 14, movable yokes made of electromagnetic substance which move together with spools 15. Each of the spools 15 is positioned according to the balance between the electromagnetic force and the output hydraulic pressure, to control the output hydraulic pressure. Reference characters P.sub.R and P.sub.M denote a transmission hydraulic pressure and a main hydraulic pressure, respectively, which are determined univocally by currents in the electromagnetic coils 12.
Further in FIG. 4, reference numeral 205 designates a V-belt; 210, an input shaft; 211, an output shaft; 224, a hydraulic pressure pump; 225, an input shaft cylinder; 226, an output shaft cylinder; and 227, an oil filter.
In the transmission control system thus organized, the hydraulic pressures of the cylinders 225 and 226 are controlled with the solenoid valves 1 and 2, to change the radii of rotation of an input shaft pulley and an output shaft pulley, over which the V-belt 205 is laid, thereby to change the speed.
FIG. 5 shows the arrangement of a control section adapted to control the application of current to the solenoid valves 1 and 2. In FIG. 5, reference numeral 100 designates a micro-computer; 101, powder clutch controller; 102, transmission hydraulic pressure controller; 103, main hydraulic pressure controller; 104, a powder clutch; 105 and 106, the hydraulic pressure solenoids of the solenoid valves 1 and 2, respectively; 108, amplifiers for amplifying output signals of the microcomputer 100; 109 and 113, vehicle indication lamps; 110, a warning buzzer; 111 and 112, control solenoids; 114, waveform shaping circuits for shaping pulse signals outputted by a vehicle speed sensor, a clutch number-of-revolutions sensor, and an engine number-of-revolutions sensor, respectively; 115, an A/D (analog-to-digital) converter for converting analog data provided by a throttle opening sensor into digital data; and 116, an input interface circuit for engine control data switches, running control data switches, and so forth.
In the control section, a vehicle speed signal, an engine number-of-revolutions signal, and a clutch number-of-revolutions signal are provided as pulse signals, and their real signals are calculated by using the pulse periods. In addition, a transmission gear ratio is obtained from the number of revolutions of the input shaft 210 (which can be obtained from the number of revolutions of the clutch) and that of the output shaft 211 (which can be detected from the vehicle speed signal).
FIG. 6 shows the arrangement of the transmission hydraulic pressure controller 102 or the main hydraulic pressure control means 103 for controlling the application of current to the hydraulic pressure controlling solenoid valve 1 or 2. In FIG. 6, reference numeral 302 designates a D/A (digital-to-analog) converter; 303, a pulse width modulator for outputting on/off control signals according to a current instruction value Vis from the D/A converter 302, and a current feedback signal V.sub.IF ; 304, a NOT circuit; 309, a base resistor; 305, a current controlling transistor; 351, a feedback diode; 306, a solenoid corresponding to the solenoid 105 or 106 in FIG. 5; 307, a solenoid current detecting resistor; and 308, an amplifier circuit.
The microcomputer 100, receiving various rotation signals, switch signals, and analog signals, controls the application of current to the hydraulic pressure solenoids 1 and 2 thereby to control the main hydraulic pressure and the transmission hydraulic pressure of the non-stage transmission. That is, the microcomputer 100 outputs a digital signal coded with a plurality of signals by logic operation. The digital signal thus outputted is applied to the D/A converter 302, where it is converted into an analog signal; that is, the current instruction signal V.sub.IS is obtained. The D/A converter 302 needs a ladder circuit; that is, it is considerably intricate in arrangement. Thus, the use of the D/A converter is disadvantageous in mounting density and in manufacturing cost.
The current of the solenoid 306 is applied through the current detecting resistor 307 to the amplifier circuit 308, where it is amplified into the aforementioned current feedback signal V.sub.IF. The current feedback signal V.sub.IF and the current instruction signal V.sub.IS are applied to the pulse width modulator 303, where they are compared with each other to form the on/off control signal. When the current control transistor 305 is conductive (on), current is allowed to flow in the solenoid 306 through the transistor 305. When, on the other hand, the transistor 305 is non-conductive (off), current is allowed to flow in the solenoid 306 through the current detecting resistor 307 and the feedback diode 351.
The conventional control circuit is designed as described above, needing the D/A converter 302. Therefore, the control circuit is unavoidably intricate in arrangement, bulky in size and high in manufacturing cost. In addition, since the current feedback signal V.sub.IF is not applied to the microcomputer 100, it is impossible for the microcomputer 100 to determine the occurrence of abnormal conditions. Furthermore, when the current in the solenoid 306 is decreased, the coil impedance of the feedback diode 351 and the solenoid 306 is decreased, and it is impossible to adjust the coil current reduction rate to improve the hydraulic pressure response.